If a US SLBM was launched, where did the nuc tip missile go????? Same with a nuc tip sub cruise missile. It takes off and lands somewhere with a mushroom cloud. Every earthquake monitor along the west coast would be kicking live. So far no indications of explosion. Furthermore major universities have ocean sonar networks for ocean and marine studies. Any water missile launch will also be recorded and detected. If it was a missile, a possible jihadist demo of a manportable SAM shot from a merchant ship???? I think that is more plausible then huge missiles fired from Chicom or US subs.
Can you say X-37B?
http://www.foxnews.com/scitech/2010/04/22/air-forces-mystery-robot-spaceship-launch-nasa/
Perhaps a sea based delivery vehicle?